1. Field of the Invention
The invention relates to a data processing device and a method of operating the same, and more particularly to a data processing device having a back-light unit driven by a battery, and a method of saving power consumption in the back-light unit.
2. Description of the Related Art
A data processing device is generally designed to include an interface, a control unit, and a display unit, wherein the control unit carries out an operation in accordance with instructions input thereinto through the interface by a user, and the display unit displays data such as characters which are results of an operation having been carried out by the control unit.
Such a data processing device as mentioned above includes a personal computer and a portable communication terminal. A personal computer displays data input thereinto by a user through a keyboard and/or results of processing the input data, on a display unit. A portable communication terminal displays data input thereinto by a user through an interface such as a key pad or push buttons and/or results of processing the input data, on a display unit.
A control unit in such a data processing device as mentioned above can be fabricated smaller and lighter because of progress in integration technology and techniques of mounting parts on a device. A display unit also can be fabricated thinner and smaller, and can display quite small characters thereon. For instance, a liquid crystal display (LCD) is usually used as a display unit in a data processing device. As a result, there have been developed many data processing devices which are portable and have high performances, and there is still a need for a data processing device having higher performances and being smaller and lighter.
A liquid crystal display used as a display unit carries out displaying by virtue of variation in an index of refraction of a light, and hence, it is necessary to illuminate a liquid crystal display from the back thereof by means of a back-light unit. A back-light function can be accomplished, for instance, by driving a light-emitting device. As such a light-emitting device, there is usually used a light-emitting diode.
A back-light unit has to be kept driven while a liquid crystal display is in operation. Hence, a current has to be kept supplied to a liquid crystal display in accordance with light-emission of the liquid crystal display. As a result, power consumption of a back-light unit occupies a high weight in overall power consumption of a data processing unit.
In a data processing device such as a portable communication terminal and a cellular phone, an interface is illuminated from the back thereof in order to assist a user to handle the interface.
As mentioned so far, a data processing device is generally designed to include a back-light unit for various purposes which back-light unit consumes much power. On the other hand, it would be necessary to be able to drive a data processing device with a battery as long as possible in order to ensure portability of a data processing device. To this end, it is necessary to reduce overall power consumption of a data processing device. Hence, many attempts have been made to reduce power consumption of a data processing device having a back-light unit.
FIG. 1 is a block diagram of one of conventional data processing devices. The illustrated data processing device constitutes a portable communication terminal, and is comprised of an interface 10 including keys, an output unit 11 displaying an operation carried out by the interface 10 and results of such an operation, a back-light unit 12 including a plurality of light-emitting devices and illuminating the interface 10 or the output unit 11, a timer unit 13 controlling a period of time in which the back-light unit 12 is turned on, a battery 14 supplying electric power to parts constituting the data processing device, a detector 15 detecting residual power of the battery 14, a table 16 storing the number of the light-emitting devices to be turned on in accordance with the residual power of the battery 14, detected by the detector 15, and a controller 17 controlling operations of the above-mentioned parts constituting the data processing device.
In operation, when a predetermined key in the interface 10 is actuated to thereby cause the battery 14 to supply electric power to the parts of the data processing device, the controller 17 turns the back-light unit 12 on to illuminate the interface 10 and the output unit 11. The controller 17 always monitors the residual power of the battery 14 detected by the detector 15, and turns on the light-emitting devices for a predetermined period of time measured by the timer 13 by the number dependent on the detected residual power of the battery 14. After the predetermined period of time has passed, the controller 17 turns off the light-emitting devices.
The data processing device illustrated in FIG. 1 reduces power consumption in the above-mentioned manner to thereby enable the data processing device to operate as long as possible.
FIG. 2 illustrates an example of the table 16. As illustrated in FIG. 2, the table 16 stores the number of the light-emitting devices to be turned on among all of the light-emitting devices constituting the back-light unit 12, in dependence on the residual power V of the battery 14, detected by the detector 15.
For instance, if the residual power V of the battery 14, detected by the detector 15, is smaller than a first threshold voltage V1, but equal to or greater than a second threshold voltage V2, M2 light-emitting devices are turned on among all of the light-emitting devices constituting the back-light unit 12.
The controller 17 is designed to include a central processing unit (CPU), and carries out such a control as mentioned above in accordance with a control program stored in a memory such as a read only memory (ROM).
FIG. 3 is a flow-chart of an operation to be carried out by the controller 17 in accordance with a control program stored in a memory.
The controller 17 always monitors the residual power V of the battery 14, detected by the detector 15, and first compares the detected residual power V to a first threshold voltage V1, in step S20.
If the residual power V is judged to be equal to or greater than the first threshold voltage V1 (YES in step S20), the controller 17 turns on the light-emitting devices by the number of M1 among all of the light-emitting devices constituting the back-light unit 12, in accordance with the table 16, in step S21.
If the residual power V is judged to be smaller than the first threshold voltage V1 (NO in step S20), the controller 17 then compares the residual power V to a second threshold voltage V2, in step S22.
If the residual power V is judged to be equal to or greater than the second threshold voltage V2 (YES in step S22), the controller 17 turns on the light-emitting devices by the number of M2 among all of the light-emitting devices constituting the back-light unit 12, in accordance with the table 16, in step S23.
If the residual power V is judged to be smaller than the second threshold voltage V2 (NO in step S23), the controller 17 then compares the residual power V to a third threshold voltage V3, in step S24.
If the residual power V is judged to be equal to or greater than the third threshold voltage V3 (YES in step S24), the controller 17 turns on the light-emitting devices by the number of M3 among all of the light-emitting devices constituting the back-light unit 12, in accordance with the table 16, in step S25.
If the residual power V is judged to be smaller than the third threshold voltage V3 (NO in step S24), the controller 17 turns of the light-emitting devices by a predetermined number which is determined in dependence on the residual power V.
After the controller 17 has turned on the light-emitting devices by the predetermined number among all of the light-emitting devices constituting the back-light unit 12, the controller 17 causes the timer 13 to measure a time, in step S26.
The timer 13 measures the lapse of time, and increments a period of time T at a predetermined cycle, in step S27. The controller 17 monitors the incremented time T measured by the timer 13, and judges whether the time T is over a predetermined threshold period of time T1, in step S28.
If the time T is not over the predetermined threshold period of time T1 (NO in step S28), the controller 17 keeps monitoring the time T until the time T reaches the predetermined threshold period of time T1.
If the time T is over the predetermined threshold period of time T1 (YES in step S28), the controller 17 turns off the light-emitting devices which were turned on in steps S21, S23 or S25, in step S29.
Thus, the controller 17 finishes the operation of controlling the back-light unit 12.
The data processing device having been explained with reference to FIGS. 1 to 3 is suggested in Japanese Unexamined Patent Publication No. 7-327004.
The Publication also suggests a data processing device which changes the threshold period of time T1 to vary a period of time in which the light-emitting devices are turned on, in accordance with the residual power V of the battery 14 detected by the detector 15, thereby reducing power consumption in the data processing device.
Though only the back-light unit 12 for illuminating a display unit or an interface from the back thereof has been explained so far, the explanation about the back-light unit 12 is also applied to a side-light unit (not illustrated) for illuminating a display unit or an interface from the side thereof.
With development in communication network, a data processing device as mentioned above is designed to have a function of making communication. Such a data processing device has to transmit radio signals for making communication with other communication terminals such as a cellular phone, for instance, in the personal digital cellular (PDC) system (RCR STD-27) standardized as a standard digital cellular phone system in Japan. In general, transmission of a radio signal consumes much power.
Hence, a data processing device having a back-light unit and a function of making radio communication has to include a battery having a capacity sufficient to supply a current to drive the back-light unit and carry out the function of making radio communication, even if the technique suggested in the above-mentioned Japanese Unexamined Patent Publication No. 7-327004 is applied to the data processing device. A data processing device has to further include a power supply circuit associated with the battery.
Hence, as the battery has to be fabricated larger in size, the power supply circuit has to be fabricated larger in size, resulting in problems of incapability of designing a data processing device to be smaller and lighter, incapability of ensuring portability, and an increase in fabrication cost.
A data processing device having a back-light or side-light unit and another unit for carrying out a certain function such as a function of making radio communication would be accompanied with the above-mentioned problems.
Japanese Unexamined Patent Publication No. 4-263305 has suggested a portable terminal having a liquid crystal display unit, comprising first means for detecting that any data is not displayed on the liquid crystal display unit for a predetermined period of time, second means for interrupting power supply to the liquid crystal display unit when the first means has detected that any data is not displayed on the liquid crystal display unit for the predetermined period of time, third means for detecting whether a user makes a touch with the liquid crystal display unit for requesting the liquid crystal display unit to re-start display, and fourth means for supplying power to the liquid crystal display unit again in response to the request of a user.
Japanese Unexamined Patent Publication No. 10-164188 has suggested a portable terminal comprising a circuit having a light-receiving device for detecting a light. Illumination to a display unit is controlled based on an output signal transmitted from the circuit.
The above-mentioned problems remain unsolved even by the portable terminals suggested in the above-mentioned Publications.